For purposes of microscopic examination of certain material, particularly cellular materials such as blood, tissue and the like, it is customary to place a smear of a liquid or substrate containing the material (e.g., a smear of plasma containing blood cells), or a thin section of the material itself (e.g., a thin slice of animal or plant tissue) on a transparent plate or slide. Thereafter, the material is stained by subjecting it to contact with solutions which stain or dye only certain constituents of the material or cells and this provides a contrast which facilitates visual examination.
Various staining procedures are utilized to produce different effects. For example, a solution can be employed to color a transparent substrate and thus provide contrast to essentially colorless cells; other solutions can be utilized to effect color differences between various parts of the cell. Solutions can be used to stain only portions of a cell, e.g., the nuclei and not the cytoplasm. In a procedure known as negative staining the cells can be caused to appear colorless against a colored background. Certain procedures are relatively simple and require the use of only a few solutions. Others, however, are complex and require successive applications of relatively large numbers of solutions.
In many of these staining procedures, certain of the solutions merely prepare or fix the substrate whereas the actual stains are made by one or more natural or synthetic dyes. The dyes selected are, of course, suited for the type of cell and the staining desired. The oxazine dyes, the triphenylmethane dyes and the thiazine dyes are examples of some families of dyes that are commonly used.
In a conventional staining procedure it has been the general practice to dip the slide successively into a series of containers holding different solutions, the slide being allowed to remain in each solution for a predetermined time interval of perhaps several minutes before removing and dipping the slide into a succeeding solution. Usually the last container holds a wash, such as water, after which the slide is dried for examination. These operations can be performed manually by a technician or in automated equipment which has been developed for such operations.
Depending upon the nature of the material being stained and the type of staining desired, as many as twelve solutions are sometimes required in the overall procedure. The fact that many slides are frequently involved merely multiples the problems. Furthermore, when successive slides are passed through the same container of solution, as in the case where dipping is employed, there is a danger of contamination of the solution. The danger increases when the same solution is used in different staining procedures for different types of materials and substrates.
In another system microscopic slides are stained by dripping stain onto the surface of a slide. Buffer is then added and an air jet is used to mix the buffer and stain on the surface of the slide. Obviously, very careful regulation of the air jet is essential in order to obtain an even distribution and mixing of buffer and stain.
In U.S. Pat. No. 3,431,886 apparatus is described for automatically applying a single liquid or multiple liquids to the bottom face of a generally horizontally disposed slide while the slide is being conveyed in spaced relation over and generally parallel with a flat liquid-applying surface. The HEMA-TEK.RTM. apparatus described in the patent and sold by Miles Laboratories, Inc. of Elkhart, Ind. has now become an industry standard for applying one or more liquids to a slide. The apparatus and system for applying liquids disclosed in U.S. Pat. No. 3,431,886 is hereby incorporated by reference.
For certain purposes, however, even further control of the application of liquids to slides has been desired in order to achieve a greater degree of control of liquid stain intensity and uniformity of application. It has also been desired to increase the speed at which slides are stained by automated equipment.